(1) Field of the Invention
The present invention relates to a developing unit, in particular relating to a developing unit for use in an image forming apparatus for performing image formation with toner.
(2) Description of the Prior Art
Conventionally, in image forming apparatuses based on the electrophotography using toner, such as copiers, facsimile machines, etc., a developer is supplied as appropriate from a developing unit to an electrostatic latent image that is formed on a photoreceptor in accordance with image information so as to visualize it, and this developer image is in turn transferred to a recording medium to thereby achieve image output.
Typically, the developer is comprised of a developer hopper for storing a developer (including toner) therein, an agitating and conveying means for conveying the developer in the developer hopper while agitating it with a screw etc., and a developing roller for supplying the developer to a photoreceptor, and supplies an appropriate amount of the developer that has been uniformly agitated in the developer hopper to the electrostatic latent image bearer (photoreceptor drum).
However, in the conventional developing unit, for example in a case where the developer is conveyed whilst being agitated with a screw etc., the developer is more likely to stagnate on the terminating end side than on the starting end side of conveyance. Accordingly, the quantity distribution of the developer inside the developer hopper becomes imbalance, or the developer tends to gather to the downstream side with respect to the direction of conveyance, causing image failures if high-speed printing is performed.
Also, since conveyance of the developer inside the developer hopper by the agitating and conveying means suffers the problem that exchange of the developer to be conveyed cannot be reliably and smoothly done, hence circulation of the developer becomes poor and the efficiency of conveyance lowers, this configuration faces difficulties in dealing with the recent high-speed trend of image output.
To deal with the aforementioned conventional problems, there has been a known configuration (see patent document 1: Japanese Patent Application Laid-open 2000-137383) which, in order to secure good circulation of the developer inside the developing hopper, includes a main conveying means for conveying the developer, made up of a first agitating and conveying means for conveying the developer in one direction inside the developer hopper and a second agitating and conveying means for conveying the developer in the direction opposite to the direction in which the developer is conveyed by the first agitating and conveying means, and arranged so that the terminating end of developer conveyance by the first agitating and conveying means and the terminating end of developer conveyance by the second agitating and conveying means are located at positions more inwards than the ends of the effective agitation and conveyance by the agitators.
However, the above-described conventional configuration not only needs a greater number of apparatus components but also increases complexity in machine structure, hence suffers difficulties in achieving space-saving.